Patent GB-620759-A (GB)
Title: Means for measuring surface areas
IPC: G01B5/26
Filed: 1946-04-02
Abstract: 620,759. Photo-electric measurement of areas. PESKIN, S., and LEMBKE, F. M. April 2, 1946, No. 10222. [Class 40 (iii)] A device for measuring surface areas of objects such as planks of timber comprises means for passing an object over an illuminated reference area, photo-electric means, for determining the proportion of the area covered by the object, and an integrating device. In one embodiment a conveyor belt 10 is taken round a wheel 11 to provide a trough 15 in which there are one or more lamps 17 evenly illuminating a diffusing screen 20. Planks of wood to be measured are fed at a predetermined rate across the reference area 19 by the conveyor and the proportion of the area obscured thereby is determined by a photo-electric cell 22 on which an image is focussed by a lens 221. A similar cell 24 is illuminated continuously by .the same lamp 17 and both feed amplifiers, see Fig. 4 (not shown), outputs of which drive electric motors connected to a differential gear and the output shaft of this drives a counting mechanism. The amplifiers are adjusted so that the differential output shaft does not move when the cell 22 is unobscured, and since the linear velocity of the conveyor is constant the counter is graduated directly in area measure. In order to prevent the admission of extraneous light a hood 48 extends over the conveyor belt and carries flexible flaps 49. If the speed of the driving motor cannot be maintained constant it is also made to drive a tachometer generator, the output of which controls the outputs of the amplifiers in proportion. An additional fitting for indicating the area of each individual object measured comprises a pointer which is automatically returned to zero by withdrawal of a pawl when an object to be measured influences a photo-sensitive device in advance of the measuring area, see Fig. 6 (not shown). The area of a batch may be determined by a manually-operated switch which prevents the automatic return of the counter. In any of the foregoing arrangements a printed record may be obtained by connecting a type head in place of the counting mechanism and actuating a printing hammer by an electrical impulse derived from the change in current flowing through the cell 22 when the end of the object leaves the reference area, see Fig. 7 (not shown). A further embodiment employs a mirror drum 119, Fig. 8, rotated in correspondence with the movement of the conveyor 10 so as to scan linear elements of the object in turn. A shutter 121 allows light to pass to the cell 22 when the image of the illuminated area is correctly aligned. In this arrangement the momentary current derived from the opening of the shutter is divided into a series of pulses by a condenser relaxation oscillator, Fig. 9 (not shown), each pulse representing an element of area, and their number in a given time indicating the total area scanned. The pulses cause stepping of a counter or printing device to indicate the total area measured. The illuminated area may also be scanned by a rotating apertured drum, Figs. 11, 12, 13 (not shown), or by an iconoscope, Fig. 14 (not shown).